A semiconductor chip, or die (such as an image sensor chip) is fabricated on a single semiconductor wafer, along with hundreds and in some cases thousands of copies of the same die. Separating a semiconductor wafer into individual dies can be done with a die saw (such as a diamond saw). Cuts are made along areas of non-functional semiconductor material separating each die known as scribe lines. However, using a diamond saw introduces mechanical stress to the semiconductor wafer and can result in cracking at the die edge and compromising the integrity and reliability of the integrated circuit. One structure used to make a die less susceptible to the mechanical stress of die saws are seal rings. A die seal ring is formed in or on an outer edge region of one or more dielectric layers of a semiconductor substrate to protect the integrated circuit from contaminants (e.g. sodium) and make a die less susceptible to the mechanical stress caused by the die saw.
As integrated circuit technologies continue to advance, there are continuing efforts to increase performance and density, improve form factor, and reduce costs. The implementation of stacked three dimensional integrated circuits have been one approach that designers sometimes use to realize these benefits. Some examples of where three dimensional integrated circuits are a suitable consideration include stacking memory on top of image sensors or processor chips, stacking memory on top of processor chips, stacking processor chips on top of image sensors, stacking chips that are fabricated with different fabrication processes, stacking two small integrated circuit chips whose separate yield may be higher than one large one, or stacking chips to reduce the integrated circuit system footprint.
However, the mechanical stresses caused by die saws when separating dies out of a stacked three dimensional integrated circuit remains a factor to be addressed. Furthermore, there is an additional weakness created at the bonding interface between the stacked wafers.